1. Field of the Invention
The present invention relates to the field of batteries, and more specifically to a method and device for charging and dispensing rechargeable batteries.
2. Description of the Prior Art
Rechargeable batteries, generally of the Nickel-Cadmium variety, (Ni-Cad batteries), are utilized with great frequency in both household and business environments. Typically, the batteries are used to power various electrical loads such as flashlights, toys, and tape recorders. A user of rechargeable batteries often has many more rechargeable batteries than can be utilized at any one time. This permits the user to discharge some of his batteries through use, while concurrently charging the remaining batteries.
There are at numerous problems encountered in the recharging of such batteries. First, many commercially available charging devices can only charge two or four batteries at any given time. In an office having numerous dictation machines, or in a home environment having numerous electrical toys, it is often useful to have the ability to charge six, ten, or a greater number of batteries at any given time.
Second, rechargeable batteries tend to be placed in various out-of-the-way storage spots when they are neither being charged nor being used. This practice leads to batteries eventually becoming misplaced.
Third, rechargeable batteries tend to spontaneously lose their charge over an extended period of time, ("power fading"). To maintain full charges on multiple batteries, a user must rotate all his batteries through a charger at regular intervals. The resulting practice of frequent switching of the batteries into and out of the charging device is both cumbersome and annoying.
Fourth, it is often desireable to vary the charging voltage and rate for different batteries. For example, where the charger is of limited power with respect to the number of batteries being charged, those batteries which are to be used next should receive the greatest voltage, while those batteries not likely to be used for some time should receive the least voltage. Many battery chargers do not have the capability to charge different batteries as different rates.
Fifth, rechargeable batteries exhibit "memory," a condition in which the batteries tend to hold only as much charge as was utilized during the previous discharge. Unless the batteries are fully discharged before they are charged, the batteries will hold progressively smaller and smaller charges over time. Many battery chargers do not have any capability for discharging the batteries prior to recharging.
The prior art shows that while attempts were made to resolve each of these problems, no one was ever successful in resolving all the problems in the same device. For example, U.S. Pat. No. 3,297,932 issued to Murphy in 1967 discloses a dispenser-charger in which serially connected batteries are advanced from a first position to a last position within a charger housing. Murphy's invention resolves the first three problems, quantity, storage and fading by charging a relatively large number of batteries within a small space. However, because the batteries are serially connected, Murphy's device cannot discharge the batteries fully before re-charging, and cannot differentially apply a higher voltage to the batteries near the last position while applying a lower voltage to those batteries near the first position. Moreover, if any of the batteries are sufficiently defective to block the flow of electricity, none of the serially connected batteries will be charged at all. U.S. Pat. Nos. 3,665,285, 4,766,361 disclose the parallel charging of batteries according to different voltages appropriate for each battery, but cannot realistically handle a large number of batteries since the batteries are not efficiently stacked, and do not advance from position to position within the charger.
3. Summary of the Invention
Accordingly, it is an object and advantage of the present invention to resolve each of the problems listed above.
In the present invention, a battery charger is configured to contain a plurality of batteries stacked parallel to one another within a housing. Batteries are preferably added to the top of the stack and removed from the bottom of the stack, such that the batteries within the stack advance from one position to another within the housing. The batteries towards the top of the stack are actively discharged by being shorted across resistors, and the batteries towards the bottom of the stack are parallely charged, or maintained at a full charge, by a voltage source coupled to the bottom of the stack. A combination of switches and position within the housing control which batteries are discharged and which batteries are charged.
The quantity, storage and fading problems are readily resolved by the efficient placement of the batteries within a device of the present invention. The batteries are stacked side by side, allowing a large number of batteries to be charged and stored at the same time, within a relatively compact charger. Differential charging of batteries is accomplished by parallely charging the batteries from a voltage source coupled to the bottom of the stack. Finally, the memory problem is resolved because the batteries can be discharged before they are charged.